Gas-powered lawn mowers need spark plug maintenance. Learn how to change, remove and clean your spark plugs to keep your machines running smoothly.
When it’s time to cut the grass, you want your lawn mower to start easily and run well. Maintaining your mower’s spark plug is an important and simple part of responsible gas-powered lawn mower ownership.
- Lawn Mower Spark Plug Function
- Checking Spark Plugs
- Cleaning Spark Plugs
- Should I Reuse My Lawnmower Spark Plugs?
- Changing Spark Plugs
Lawn Mower Spark Plug Function
Spark plugs are an essential lawn mower component that ignite the fuel-and-air mixture inside the cylinder of the mower engine. High-voltage electricity jumps the gap at the tip of every spark plug at just the right moment to trigger fuel combustion.
When spark plugs get dirty or begin to fail electrically, the quality of spark decreases, triggering incomplete fuel combustion and lower engine performance and efficiency. Taking care of spark plugs is one of the most important maintenance tasks for optimal gas-powered lawn mower performance.
Checking Spark Plugs
Begin by removing your mower’s spark plug to check it. Spark plugs are typically located on the back or side of a lawn mower engine. Look for a short wire that’s about 1/4-in.-thick leading to the top of a short, cylindrical protrusion from the engine. If you’re not sure where the spark plug is, consult your owner’s manual.
Use your fingers to pull the wire off the top of the spark plug, then use a spark plug wrench to turn the plug counterclockwise to loosen and remove it.
How does the tip look? A spark plug in good condition from an engine that’s running well will have a light gray or tan color. Any oily deposits, soot or baked-on carbon indicates that the spark plug needs to be cleaned or replaced.
Cleaning Spark Plugs
Once upon a time, spark plugs were expensive enough and small engines ran dirty enough that cleaning and reusing spark plugs was typical. I’ve cleaned many spark plugs during my motorcycling and go-karting days in the 1970s and 80s.
But even though I have dozens of engines in my life now, I almost never clean spark plugs. For $5 or $6 you can install a new plug that will work well. Still, knowing how to clean spark plugs is a valuable skill because you might not always have a new plug on hand.
Oil or carbon on the tip of any spark plug gives electricity an alternative pathway, preventing the fuel-igniting spark at the gap. That’s a problem. Cleaning usually eliminates this alternative path.
Flood the tip of the plug with rubbing alcohol to cut through any oil that might be present. Scrub the area with an old toothbrush and rinse the plug again with rubbing alcohol. Then repeat the scrubbing. If the tip of the plug doesn’t look clean after drying, repeat the process.
Should I Reuse My Lawnmower Spark Plugs?
You can, but there’s a good reason not to. Besides oil and carbon deposits creating that alternative electrical path, spark plugs can also fail electrically. This is why a used plug you’ve cleaned perfectly can still malfunction under load, failing to deliver an optimal spark inside the engine.
Changing Spark Plugs
Every reputable spark plug has a code number on the side, making it easy to buy a replacement. Different manufacturers have different codes, but all companies offer plugs that can be used interchangeably with different brands.
Place a small amount of anti-seize compound on the threads of the new plug to make the plug easier to remove next time, thread it into the engine with your fingers, then tighten an additional half or three-quarters of a turn using a spark plug wrench.
If you’ve got a lawn mower that isn’t working properly, there are ways you can tell if it’s your spark plug or another engine part that is the problem. When you’re ready to mow your lawn on a Saturday morning and you’ve got all the gear out and ready to go, the last thing you want is for your lawn mower to malfunction, depriving you of the satisfaction of your grass looking fresh and groomed to perfection.
The spark plug in a lawn mower could be bad if:
- You can’t get the engine to fire up at all
- You have to tug extra hard for longer than usual on the rewind
- Your lawn mower loses power while moving
- The gas runs out quicker than it used to
Sometimes identifying if it actually is the spark plug that is the problem can be a challenge. Read on to see what makes a spark plug go bad, how to tell if yours has reached the end of its life, how to reinstall one, and when it needs replacing.
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Signs that the Spark Plug is the Problem
Lawnmowers can have a variety of problems, and it can sometimes be difficult to diagnose which part is to blame. There are some key things to watch for that will let you know that the spark plug is the culprit.
If the engine is turning over but won’t start, the spark plug is often to blame. An overly worn or dirty spark plug will not spark as quickly and can take more work to get it functioning.
Secondly, if you’ve gotten your mower to start and then, in the middle of mowing your lawn, it dies while moving, this could be a sign that the spark plug needs some attention. Spark plugs may be inconsistent or unreliable if they are damaged or worn.
This YouTube video from Sears PartsDirect covers the basics. Although they are demonstrating on a push mower, the symptoms and solutions are the same for a riding mower:
Lawn Mower Won't Start: Spark Plug and Ignition Problems
You can also tell that you have faulty spark plugs if your fuel tank is running out of gas much faster than usual, and you have to refill it too often. The spark plug may not be burning all of the fuel if its spark is weak, allowing too much fuel to move through the chamber without being burned and utilized, thus causing you to refill it sooner.
Source: Champion Auto Parts
How to Clean and Reinstall a Spark Plug
If you discover that your spark plug is not functioning correctly, there are a few things you can do to move forward. If your spark plug is damaged or too worn down for continued use, the best option is just to get a new one. Spark plugs can cost anywhere from $2-$10, depending on where you get them and the brand or type you prefer.
If your spark plug is not damaged or overly worn down, then you could consider cleaning and reinstalling it. This is an excellent option for spark plugs that just have a little gasoline, oil, or carbon buildup on them but have the porcelain sheath intact and the electrodes still in good shape.
To start, make sure you’re working in a clean area to avoid any debris or dirt getting into the combustion chamber.
You’ll need to use a spark plug socket to remove the spark plug. This is a tool designed specifically for spark plug maintenance. It will allow you to unscrew the spark plug safely after you’ve removed the spark plug lead.
Next, you can use a soft-wire brush or a spark plug spray cleaner to gently remove anything coating the spark plug. Using a soft-wire brush is essential because any damage to the spark plug can render it unusable, so being as gentle as possible will save you time and money in the long run.
Once the spark plug has been cleaned, it can be reinstalled in the mower, reversing the steps taken to remove it. Use the spark plug socket as needed and be sure not to overtighten the spark plug.
Sources: infobase, Dummies.com
How Long Does a Lawn Mower Spark Plug Last?
Spark plugs are an item that needs regular replacing, no matter how well-maintained they are by the user. How often they need to be replaced depends on how often the lawn mower is used each season.
Typically, the consensus among the mechanical engineer community is that a spark plug for a lawn mower will last up to 25 hours of use.
Some users simply prefer to replace it every mowing season as a part of their yearly lawn mower maintenance. If you use it for the full 25 hours each season, this is a great option to ensure you don’t run into spark plug problems.
If you aren’t sure that your season requires 25 hours of mowing, then perhaps tracking the hours you use the lawn mower could help you determine how often to replace the spark plug.
Source: besthomegear.com
What Makes a Spark Plug Go Bad?
There are many parts of a small engine that are made to last through the lawn mower’s lifetime. They are hardy and can withstand a lot of wear and tear. Spark plugs are not one of those parts, unfortunately. They are not made to last through long term use.
All spark plugs eventually wear out and need replacing. It’s the nature of the item, and it’s unavoidable.
Spark plugs go bad because the electrodes at the bottom wear down with each use, making them shorter and shorter until they are no longer long or sharp enough to create the necessary spark to get the engine running.
If the spark plug is not worn down, though, and is still malfunctioning, then it could be due to other factors, such as:
- Overheating: When a spark plug overheats, it can cause the ignition spark to be weaker by widening the space between the electrodes and the center of the plug.
- Damage to the Electrodes or the Porcelain Sheath: The structural integrity of a spark plug is essential to its functionality, and if any part of that is scratched, cracked, chipped, or worn too much, then the spark plug will not function properly.
- Buildup of Carbon around the Plug: When there is too much debris getting into the area where the spark plug is igniting, it can cause buildup around the plug and make it less effective.
- Oil Fouling the Tip of the Plug: This is something that can happen if the spark plug has been worn and overused. Oil can get into the combustion chamber and can prevent the spark plug from working properly.
If any of these issues are present, they can cause a spark plug to be less effective or completely useless.
Sources: Manitoba University, Champoinautoparts.com,
Conclusion
A bad spark plug is a simple fix on a lawnmower. You can often clean the plug and get it back into running shape but they are relatively inexpensive so if there is any doubt, just replace it and move on.
Did that fix your problem? If not, look through this troubleshooting guide that I put together when my John Deere lawn mower wouldn’t keep running. The troubleshooting steps are pretty much the same for any mower.
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Paul has a two-acre yard on red clay soil in Southeast Texas. He knows exactly what the challenges are to nurturing a thriving yard in difficult soil.He takes a practical approach to yard improvement and enjoys putting best practices and “golden rules of lawn care” to the test.